sql: add telemetry for schema changer mode

[rafiss]

sql: use featureflag check for new schema changer

Now the check uses the statement tag to determine which operation is
running.

I took the opportunity to make sure the statement tags matched with the
ones Postgres returns.

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sql: add telemetry for schema changer mode

fixes #99386

This adds feature counter telemetry as well as log based telemetry to
indicate which version of the schema changer was used.

The telemetry keys are:

• sql.schema.schema_changer_mode.legacy
• sql.schema.schema_changer_mode.declarative

The new field in the log-based telemetry is:

• SchemaChangerMode

Release note: None

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[chengxiong-ruan]

create function has a similar trick since it's not opaque and have to go through optbuilder at the moment:

cockroach/pkg/sql/opt_exec_factory.go

Line 1894 in f2fa926

if plan != nil {

Maybe better to do the counting in p.SchemaChange method, or I'm good with adding an extra counting there as well.

[rafiss]

thanks for pointing that out! i added tests for it, and moved the logic to p.SchemaChange

i noticed a few more places with missing telemetry, so made a followup PR: #105482

[rafiss]

bors r+

[craig]

Build failed:

• Bazel Essential CI (Cockroach)

[rafiss]

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

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error creating merge commit from a34ef58 to blathers/backport-release-22.2-105108: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.2.x failed. See errors above.

---

error creating merge commit from 6192117 to blathers/backport-release-23.1-105108: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 23.1.x failed. See errors above.

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_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}